Method of making retroreflective material

ABSTRACT

A COMPOSITE RETROEFLECTIVE MATERIAL IS PREPARED BY DEPOSITING ON A MOLDING SURFACE HAVING CUBE CORNER RECESSES A FLUID MOLDING MATERIAL IN AN AMOUNT SUFFICIENT TO FILL THOSE RECESSES. A PREFORMED BODY MEMBER IS APPLIED THERETO AND THE MOLDING MATERIAL IS HARDENED AND BONDED TO THE BODY MEMBER. AS A RESULT, RETROEFLECTIVE MATERIAL IS PROVIDED WITH A BODY PORTION HAVING ONE SMOOTH SURFACE AND ANOTHER SURFACE FROM WHICH PROJECT A MULTIPLICITY OF SEPARATELY FORMED, MINUTE CUBE CORNER FORMATIONS HAVING SIDE EDGE DIMENSION OF LESS THAN 0.025 INCH. THE CUBE CORNER FORMATIONS MAY THEN HAVE APPLIED THERETO A RETROREFLECTIVE COATING, AND AN ADHESIVE LAYER AND RELEASE PAPER MAY BE SUPERPOSED THEREON TO PERMIT FACILE MOUNTING ON A SUPPORT SURFACE.

May 14, 1974 w. P. ROWLAND METHOD OF MAKING RETROREFLECTIVE MATERIAL Original Filed Sept. 29, 1970 United States Patent 3,810,804 METHOD OF MAKING RETROREFLECTIVE MATERIAL William P. Rowland, Southington, Conn., assignor to Rowland Development Corporation, Kensington, Conn.

Original application Sept. 29, 1970, Ser. No. 76,551, new

Patent No. 3,684,348. Divided and this application Feb.

25, 1972, Ser. No. 229,378

' Int. Cl. B29b 3/00 US. Cl. 156-245 13 Claims ABSTRACT OF THE DISCLOSURE A composite retroreflective material is prepared by depositing On a molding surface having cube corner recesses a fluid molding material in an amount sufficient to fill those recesses. A preformed body member is applied thereto and the molding material is hardened and bonded to the body member. As a result, retroreflective material is provided with a body portion having one smooth surface and another surface from which project a multiplicity of separately formed, minute cube corner formations having a side edge dimension of less than 0.025 inch.

. The cube corner formations may then have applied thereto a retroreflective coating, and an adhesive layer and release paper may be superposed thereon to permit facile mounting on a support surface.

CROSS REFERENCE TO RELATED APPLICATION The present application is a division of my co-pending application Ser. No. 76,551 filed Sept. 29, 1970, now United States Letters Pat. No. 3,684,348 granted Aug. 15, 1972.

BACKGROUND OF THE INVENTION Various reflective materials are commonly employed for safety and decorative purposes. One of the most common principles employed is simply to appl a reflective coating upon a surface of the item or to construct the item of a highly reflective material such as polished metal. In addition to reflective coatings and specular surfaces, it is also common to use structures which have upon one or both surfaces various formations which reflect the light rays impinging thereon, either principally as a result of the steepness of the angle at which the light ray impinges thereon or by virtue of reflective coatings on the surface of the formations. There has been a constant demand for retroreflective materials, i.e. materials capable of reflecting the bulk of the light rays impinging thereon in a substantially parallel path back toward the source of the light. Minnesota Mining' and Manufacturing Company has sold a material under the trademark Scotchlite which relies upon minute glass spheres embedded in a matrix of synthetic resin to provide such retroreflection. Another type of retroreflective element has a molded member having cube corner formations on one surface thereof, such molded members being formed from glass or synthetic plastic. Indicative of the efforts' to use cube corner formations for retroreflective structures are Straubel US. Pat. No. 835,648 granted Nov. 13, 1906; Hedgewick et al. US. Pat. No. 3,258,840 granted July 5, 1966; and lungersen U.S. Pats. No. 2,310,790 granted Feb. 9, 1943 and No. 2,444,533 granted July 6, 1948.

Cube corner reflectors molded from glass and more recently from acrylic resins have commonl been employed as safety devices on bicycles, automobiles and other vehicles. Although it has been suggested that the cube corner might be of small dimension, generally such ice formations have been of appreciable size and the nature of the material from which the reflector has been fabricated has resulted in structures which are relatively rigid in character and which do not lend themselves either to shaping to various substrates of nonplanar character or to use as a fabric which might be worn. Moreover, as the size of the cube corner formations is reduced, criticality in control of angles and dimensions becomes far more acute since even a minute deviation will produce a substantial deviation in the capability of the material to retroreflect light rays impinging thereon.

Accordingly, it is an object of the present invention to produce novel retroreflective material having minute closely spaced cube corner formations which return the great preponderance of light rays entering the front surface thereof.

It is also an object to produce such retroreflective material which is relatively flexible so as to permit shaping to conform to support surfaces of various configurations and to permit utilization as a fabric for application to, or formation into, wearing apparel.

Another object is to produce such retroreflective material having an adhesive coating by which it may be conveniently adhered to a support surface.

Still another object is to provide a novel method for manufacturing such retroreflective material from synthetic resins in a manner which permits selection of resins affording optimum characteristics.

A further object is to provide such a method which is relatively simple and economical and which lends itself to a high degree of control in insuring optimum development of the cube corner formations.

SUMMARY OF THE INVENTION It has now been found that the foregoing and related objects may be readily attained by a method for making retroreflective composite synthetic plastic material including several steps. A hardenable molding material is deposited upon a mold surface having an array of minute, contiguous cube corner recesses therein, each of the recesses having a maximum side edge dimension of less than about 0.025 inch. The molding material is essentially transparent and is suflicient in amount and fluidity to fill the recesses essentially completely under the conditions of operation. A preformed body member of essentially transparent synthetic resin and having substantially smooth and parallel surfaces is applied to the molding material on the mold surface under sufficient pressure to effect intimate surface contact therebetween.

The molding material is subjected to conditions sufficient to effect substantial solidification thereof and bonding to the adjacent surface of the body member to form a composite material. Then, the composite material is removed from the mold surface to provide a retroreflective material comprising a body portion having a substantially smooth front surface provided by the preformed body member and a multiplicity of minute cube corner formations corresponding to the recesses and closely spaced about and projecting from the opposite surface of the body portion. The close spacing substantially avoids any flat areas between the cube corner formations so that the light rays entering the composite material through the front surface of the body member predominately pass through and into the cube corner formations by which they are then reflected back through the composite material along a path substantially parallel to the path of entry.

The method of manufacture may include an additional step in which a reflective coating is deposited on the faces of the cube corner formations. An adhesive layer may then be deposited on the reflective coating, and a removable piece of sheet material may be loosely adhered to the adhesive layer. Thus, the removable sheet material may therefater be removed to adhere the retroreflective material to a substrate. Most desirably, the reflective coating is a metallic deposit and a layer of resin is deposited on the metallic coating to provide protection therefor. The body member most desirably is flexible for mounting of the composite material on surfaces of various configuration.

The molding material may be a molten resin and the 1 solidification thereof accomplished at least in part by cooling, the inherent nature of the molten resin producing bonding to the body member thereof. Alternatively, the molding material may be a fiuid resin having crosslinkable groups and the solidification thereof may be accomplished at least in part by cross-linking ofthe resin. In still another embodiment, the molding material may be a fluid'partially polymerized-resin formation and wherein the solidification "thereof is accomplished at least in part by polymerization of the resin formulation.

Preferably, the mold surface is metallic to provide optimum development of the cube corner formations. Most desirably,'the preformed body member is applied With suflicient pressure to distribute substantially uniformly the molding material over the mold surface to achieve a 1 substantially uniform thickness for the composite material. In this manner, a substantially uniform thickness is achieved for the body portion of the composite structure.

As will be appreciated, the retroreflective synthetic plastic material is comprised of a body portion having substantially smooth surfaces on opposite sides thereof and a multiplicity of minute cube corner formations closely spaced about and projecting from one of the smooth surfaces. The cube corner formations each have three faces and a base adjacent the body portion with a side edge dimension of not more than 0.025 inch and the close spacing avoids any substantial smooth areas therebetween. The body portion and the cube corner formations are separately formed from essentially transparent synthetic plastic resin and are bonded together into a composite structure wherein those light rays entering into said material through the opposite surface of the body portion predominately pass through the body portion and into the cube corner formations by which they are reflected back through said composite structure substantially parallel to the path of entry.

In the most conveniently formed structure, each cube corner formation has one face parallel to one face of every other cube corner formation. Preferably, the cubecorner formations are substantially equal in size and arranged in a pattern of rows and columns. The center-to-center spacing between cube corner formations in every row and between cube corner formations in every column is in accordance with a uniform pattern to insure close spacing of the formations and good retrorefiection. The apex of each cube corner formation is in alignment with the apices of all the cube corner formations located in the pattern row and column in which it is disposed, and each apex iS vertically aligned with the center of its base.

To provide optimum reflectivity, the composite material has a reflective coating deposited on the cube corner formations, thus permitting it to be placed in intimate contact with support surfaces since the air interface is no longer required for reflecting the light rays.

DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary rear view of composite rctropaper DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS M Turning first to FIGS. 1 and 2 of the attached drawing, therein illustrated is composite retrorefiective material embodying the present invention and comprised of a body portion generally designated by the numeral '10 and a multiplicity of cube corner formations generally designated by the numeral 12. The body'port ion 10' lias" two parallel smooth surfaces 14 and 1 6,theYs urface 16 having bonded thereto the cube corner formations 12. v

As best seen in FIG. 1, thecube corner.,formatio,ns 12 each have three planar faces 18 which are disposed in planes perpendicular to each other and intersecting along side edges 20'. The apex 22 of each formation is vertically aligned with the center of the base 24 thereof as is best seen in FIG. 2. The cube corner formations 12'a're arranged in a pattern providing rows and columns, and the center-tocenter spacing between the apices 22of the cube-corner formations 12 along the.rows and columns is in accordance with a regular pattern to insure close spacing and avoid substantially any flat areas therebetween.

Since the cube corner formations 12 new configured, a light ray R entering the front surface 14 of the composite material passes through the body portion 10 and into a cube corner formation 12. When it strikes one of the planar faces 18, it is directed to another of the planar faces 18 which in turn reflects the ray to the third planar face 18. The ray is then directed out the cube'corner formation 12 in a return path so that' its path back through the body portion 10 and out through the front surface '14 is substantially parallel to its path of entry. This is the principle of retroreflection; as ,a result, it is extremely critical that the dimensions and angles of the cube corner formations 12 be closely controlled.

Turning now to FIG. 3, therein illustrated is an embodiment of the invention wherein the basic composite material includes further elements to permit its affixationtq support surfaces by adhesion. The basic composite material of FIGS. 1 and 2 is employed herein and'thereference numerals are the same. A reflective coating 30 is applied to the surface of the cube corner. formations 12 conveniently by metallizing or by applying a suitable lacquer thereto. Deposited over the backsurface of the composite material is a coating 32 of an ever tacky adhesive anda release paper 34 is then loosely adhered thereon.l ,To mount this structure on a suitable surface, the release paper .34 is removed and the composite material ispressed theredimension of up to 0.025 inch, the preferred structures utilize a side edge dimension of not more than 0.0l0inch andmost desirably on the order of 0.004-0.008 inch.

The thickness of the body portion of the composite structure may vary considerably depending upon'the application. Generally, it is preferred to use -,sheet material having a thickness of 0.002-0.030 inch and mostdesirably about 0.003-0.010 inch. However, for some applications thicker structures may be desirable and so a preformed body member of substantially greater thickness may be employed andit may be made by injection molding, casting, or other techniques. 1 H v By constructing the composite material from a separate body portion and to which are adheredthe'separately formed cube corner formations, it. is possible .to achieve the maximum control over the cube corner formations and also to selected different resins'for the two om fjQ-nfi l ft- Although his theoretically possible to emboss the cube 1 corner formations into the surface of preformed synthetic plastic material, efforts to utilize such a technique in the production or minute cube corner formations of the type used in the present invention have proven unsatisfactory. Any aberration in flow of the material into the recesses of the embossing member will greatly aifect the retroreflectivity of the resultant product. Moreover, variations in thickness of the preformed material which is embossed tend to affect the precision with which the cube corner formations may be developed. Efforts to mold the cube corner formations and the body portion of the product simultaneously have also proven generally unsatisfactory because of the difficulty in obtaining adequate control'of the thickness of the web and optimum'characteristics in thisproduct. Moreover, such a procedure requires that the same resin be employed for the twoportions of thje over the development of the cube corner'formations and in permitting a selection of distinct resins for the body portion and for the cube corner formations. In this process, a mold surface is produced having precisely formed cube corner recesses which are so closely spaced as to avoid substantially any smooth areas therebetween. Al-

though the mold may be formed from a synthetic resin,

the preferred mold has ametallic surface to ensure very smooth/precise surfaces on the cube corner faces and to 'minimize the likelihood of deterioration during extensive use, as well as of possible adhesion between the molding material and the surface of the mold. Accordingly, the mold may be fabricated directly from a suitable metal by engraving, hobbing or otherwise forming the cube corner recess therein. Alternatively, a suitably engraved or otherwise formed metallic member may be used as a master "mold for forming the desired mold element by the deposition of metal thereon to form a layer of suificient thickness which is then stripped'therefrom. Exemplary of a suitable techniqueis the conventional electroforming procedure. These stripped impressions are then used as the mold elements, most desirably after mounting upon a suitable support surface to ayoidinjury thereto. In order to rninimize cor'ro'sion of the metallic surface of the mold it has been found desirable to provide'a highly inert metallic coatingthereon' sueh as maybe obtained by depositing gold'or a gold alloy thereon.

" Various synthetic resins may be employed for; the cube as cellulose acetate, cellulose ac'etate/butyrate copolymer's and" cellulose propion'ate; vinyl halides "such as polyvinyl chloride and polyvinyl fluoride; vmylidene halides such as polyvinylid'ene chloride; monovinylidene aromatic hydrocarbon polymers such as polystyrene and"styrene/acrylonitrile copolymers; ethyleni- "cally unsaturated nitriles such as polyacrylonitrile; polycarbonates; poly-esters such asp'olyethylene terephthalate;

'polyphenylerie oxide: polysulfon'es; and polyolefins such as polyethylene and polypropylene Interpolymers of varicomposite structure will vary depending upon the application', the thickness desired forj the body member, the desire for flexibility, and'need for achieving interadhesion Itherebetween'. For outdoor applications, materials which are moisture resistant, ultraviolet resistant and abrasion resistant are particularly advantageously employed at least for the body portion since that portion is generally ex- "posed to the'atmosphere and requires goodw'eathering characteristics. Moreover, 'it will be appreciated that the orrierjfbrmatiodsand for the body portion, including 7 polymers of (alk) acrylic acid esters such as polymethyb fmethacrylatej'and polybutyl acrylate; cellulose e'sters' such body portion itself may be a composite of two different synthetic resins.

The resins preferably employed for the body portion include polyvinyl halides, polyethylene terephthalate, polyvinylidene chloride, polycarbonates, polysulfones and cellulose ester polymers. The resins preferably employed for the cube corner formations comprise (alk) acrylic acid ester resins, acrylic-modified vinyl choride resins, vinyl chloride/vinyl acetate copolymers, ethylenically unsaturated nitrile resins, monovinylidene aromatic hydrocarbon resins, olefin resins, cellulose ester resins, polysulfone resins, polyphenylene oxide resins and polycarbonates. Exemplary combinations for the body portion/cube corner formations include polyvinyl chloride/ acrylic modified polyvinyl chloride; polyvinyl fluoride/polyvinyl chloride; polycarbonate/polycarbonate; polyvinyl chloride/polymethyl methacrylate; polysulfone/polymethyl methacrylate; polysulfone/polyvinyl chloride; and polyethylene terephthalate/polymethyl methacrylate.

In selecting the molding materials employed for the present invention, it should be remembered that long lasting properties will require resins which do not have readily volatilizable plasticizers or other components and which have an acceptable level of light stability. Thus, stabilized formulations are desirably employed when the resin itself is susceptible to light or oxygen degradation. By proper selection of the resin systems, the body portion also may provide a valuable degree of protection for the resin of the cube corner formations which may exhibit relatively poor stability when the cube corner formations are reflectively coated and further coated with a lacquer and/ or adhesive, these coatings also may act as protective layers since the body portions in many applications will serve as a barrier layer for ultraviolet radiation, vapor, gases etc. Moreover, the body portion is desirably fabricated of a resin which affords a high degree of abrasion resistance since aberrations in the front surface of the composite material will greatly reduce its reflectivity.

It shonld'be appreciated that the selection of different resins for the two component portions of the product must recognize'the need for compatability of the two resins. For

example, one resin must not contain a substance which is deleterious to the other and which will migrate thereinto across the interface. Moreover, when plasticized materials are employed, it is desirable to use plasticizers which do not readily migrate and/or to select formulations for both component resins in which the plasticizer contents are balanced so as to avoid a degree of migration therebetween'which might materially'affect the properties of the component portions.

.In the method, efforts are made to minimize any discrepancies in thickness and to minimize the thickness of any web portion formed of the resin utlized in the production' of the cube corner formations. Conveniently, this is accomplished by the application of pressure at the time that the body member is placed upon the mold surface so that excess resin is distributed evenly at the interface and to some extent expressed or extruded outwardly of the interface. Moreover, the application of pressure facilitates the flow of the fluid molding material into the recesses of the mold surface. The technique utilized for achieving solidification of the molding material will vary with the particular moldng material selected, the process characteristics desired and the ultimate properties sought. As a result, versatility in process design as well as product properties is readily obtained in the present invention. Moreover, because there is versatility, the process selected may be one enabling minimal equipment cost for limited production.

When a molten synthetic resin is employed as the fiuid molding material, solidification may be accomplished merely by cooling thereof; this may be accomplished through chilling of the mold, by directing cool air against the" surface of the body member or by allowing the heat energy to radiate therefrom. When the molding material is a B-stage or partially polymerized resin, solidification may be accomplished by the application of heat for a period of time sufficient to achieve the desired degree of polymerization. When the molding material is a cross linkable formulation, solidification may be accomplished by promoting cross linking of the component materials through any convenient means dependin'g upon the nature of cross linkage material. As is well known in the art, cross-linking may be effected by use of free radical initiators, heat, high energy radiation and the like. Moreover, it will be appreciated that the molding material may be essentially monomeric in character and that the solidification thereof may be accomplished by polymerization in situ within the cube corner recesses of the mold surface; such polymerization may be promoted by heat, free radical initiators, or high energy radiation. In still another technique, a plastisol formulation may be employed in which the resin particle are fluxed by the plasticizer upon the application of heat and fire into a solid structure. Obviously, combinations of these techniques also may be used to obtain the desired solidification.

It will be readily appreciated that the cube corner formations must have smooth surfaces and that the intersecting faces thereof should provide essentially perfect cube corners. Any aberration from a perfect cube corner or surface irregularity will materially reduce the retroreflectivity of the cube corner formation.

Normally, the air interface at the cube corner formations will be relied upon for retroreflection of the light rays. Obviously, the angle at which the light rays strike the faces of the cube corners will be determinative of whether the ray is retroreflected or passes outwardly through the surface. If the angle of incidence is less than the critical angle for the resin employed, the light ray will not be retroreflected. However, the bulk of the light rays, i.e., the predominant portion thereof, entering into the front surface of the sheet material, will be retrorefiected by the cube comer formations.

The reflectivity of the cube corner formations can be enhanced by depositing a reflective coating thereon. This reflective coating is conveniently provided by metallizing techniques such as those wherein a very thin film of aluminum or other metal is deposited on the surface by vaporization thereof at very low sub-atmospheric pressures. Chemical deposition techniques mayv also be used to produce a reflective metallic coating. Another technique for achieving reflective coatings is to utilize a lacquer containing metallic particles or other pigments affording a high degree of reflectivity; for example, pearl lacquers may be employed. In still another technique, the reflective coating may be provided by a metallized synthetic plastic film which is brought into intimate contact with the surface of the cube corner formations.

When a metallic coating is provided, it is customary to utilize a very thin deposit thereof because of cost considerations as well as the desire to avoid interference with the flexibility of the preferred products. To protect the thin metallic deposit from possible injury during processing, handling and use, it is customary to deposit a protective resin coating thereover, conveniently by spraying or roller coating a lacquer formulation onto the metallic surface.

As has been previously indicated, the adhesive coating upon the reflectively coated composite material offers the advantage of permitting the retroreflective material to be mounted on various support structures where reflectivity may be desired. Although various types of adhesives may be employed, ever tacky adhesives of the type conveniently used in the manufacture of pressure sensitive tapes have proven particularly advantageous. There adhesives may be applied either in solvent systems or as aqueous emulsions, depending upon the particular resin forming the base thereof.

In order to facilitate handling and shipping, afreadily releasable sheet material is applied over the surface of Example 1 Anengraved master plate was formed from aluminum using a cutting tool which generated a pattern of cube corner formations substantially as illustrated in FIGS. 1 and 2. Electroforms of nickel were then. prepared therefrom and assembled into a larger mold surface in which the cube corner recesses were closely spaced and had a depth or vertical height of 0.00235 inch and a side edge dimension of 0.0056 inch.

Onto the surface of the mold assembly is deposited a volume of vinyl chloride/vinyl acetate copolymer plastisol formulation containing monomeric plasticizers and 10.0 percent of a cross linkable acrylic resin. The resin formulation was placed in a line along one end of the mold surface. Onto the surface of the mold and volume of resin formulation was then applied a length ofpolyvinyl chloride film of about 0.012 inch thickness and pressure was applied to the outer surface thereof by means of a roll to bring about intimate contact with the resin formulation and to distribute that formulation uniformly over the mold surfaces as the film was rolled into contact therewith. The resin formulation filled the recesses completely and excess material was expressed from the end of the film. After proper orientation of the resin formulation and film, the assembly was exposed to radiant heaters to elevate the temperature of the resin formulation to about 350 Fahrenheit for about one minute to flux the formulation and cross link the acrylic resin component. The heating was discontinued and the assemblyallowed to cool, after which the composite structure was removed from the mold surface.

I Upon removal, examination under a microscope indicated that the surface of the' film had minute cube corner formations bonded thereto in close array as illustrated in FIGS. 1 and 2 of the attached drawing. The composite sheeting was highly flexible and could be readily utilized for fabric applications. Upon testing with a controlled light source, it was found that it was highly retroreflective within a narrow cone over angles of incidence to the front surface up to 45 This material was tested for reflective applications in the form of hang tags, welting, flags and was found to provide a high degree of reflection and attention gathering.

Example 2 The procedure of Example 1 was substantially repeated, exceptthat'a 0.002 inch film of polyvinyl fluoride and a cross-linkable acrylic molding formulation were eniployed. Heat was used to effect polymerization and.cross linking of the molding formulation. The resultant product was found to be retroreflective and similarly suited for diverse applications.

' Although the cube corner formations in the illustrated embodiments have a uniform orientation within the pattern, it is possible to employ a pattern in' which some of the cube corner formations have their faces disposed in a manner so that their faces are not parallel to any 'of the faces of the adjacent cube comer formationsrlna'nother embodiment, the apex of some of the cube corner formationsfis' not vertically aligned with the center of its base; by thus tipping some of the cube corner formations, rctroreflectivity over a broader angle is'pr'ovided for certain applications while maximum retroreflectivit'y is diminished. For example, highway signs desirably may exhibit retroreflection over a broader angle to the surface of the sign, and some light scattering may desirably be provided although the light rays falling thereon may be essentially perpendicular to its face.

By fabricating the preformed body portion of a relatively flexible resin, conveniently in the form of sheet material, the composite structure may be readily shaped to various support surfaces, such as the corners of hand rails, buildings and the like. Moreover, since the composite structure may be very thin and highly flexible, it may be readily applied to fabrics used as garments or it may itself be used in such a manner, thus affording a great deal of visibility to the wearer. Exemplary uses for safety applications are tabs and stripes on jackets and rainwear, tags that may be worn at various points upon the body, reflective patches for hats, reflective welting for the production of various garments, etc.

Accordingly, it can be seen from the foregoing detailed specification that the method of the present invention provides a composite material which is highly retroreflective and employs minute, closely spaced cube corner formations which return the great preponderance of light rays entering the front surface thereof. The composite material may be relatively flexible so as to permit shaping to conform to support surfaces of various configurations and also to permit utilization as a fabric for application to, or formation into, wearing apparel. In accordance with one embodiment, a self-adhering structure may be provided through utilization of an adhesive coating. The composite material may be readily manufactured from "the various synthetic resins to permit selection of resins affording optimum characteristics for the components thereof. The method is relatively simple and economical and lends itself to a great deal of control for ensuring optimum development of cube corner formations.

We claim:

1. In a method for making retroreflective composite synthetic plastic material, the steps comprising:

(A) depositing a hardenable molding material upon a mold surface having an array of minute, contiguous cube corner recesses therein, each of said recesses having a maximum side edge dimension of less than about 0.025 inch, said molding material being essentially transparent and suificient in amount'and fluidity to essentially completely fill said recesses under the conditions of. operation;

(-13) applying a preformed body member of essentially transparent synthetic resin and having substantially smooth and parallel surfaces to said molding material on said mold surface under sufficient pressure to effect intimate surface contact therebetween;

-(C) subjecting said molding material to, conditions suflicient to effect substantial solidification thereof and bonding to the adjacent surface of said body member to form a composite structureyand (D) removing said composite structure from said mold surface to provide a retroreflective composite material comprising a body portion provided by said preformed body member and having a substantially smooth front surface, and a multiplicity. of minute cube corner formations corresponding to said recesses and closely spaced about and projecting from'the opposite surface of said body portion, said close spacing substantially avoiding any smooth areas between said cube corner formations, so that those light rays entering said composite material through the front surface of said body portion predominately pass through and into said cube corner formations, by which they are reflected back through the body portion along a path substantially parallel to the path of entry.

2. The method in accordance with claim 1 wherein there is included the additional step of depositing a re 10 tflective coating on the faces of said cube corner formations.

'3. The method in accordance with claim 2 wherein there are included the additional steps of depositing an adhesive layer on said reflective coating and loosely adhering a removable piece of sheet material on said adhesive layers, whereby said removable sheet material may thereafter be removed to adhere said retroreflective material to a substrate.

4. The method in accordance with claim 2 wherein said reflective coating is metallic and wherein there is included the additional step of depositing a layer of resin on said metallic coating to provide protection therefor.

5. The method in accordance with claim 1 wherein said body member is flexible for mounting of the composite material on surfaces of various configurations.

6. The method in accordance with claim 1 wherein said milding material is a molten resin and the solidification thereof is accomplished at least in part by cooling, the inherent nature of said molten resin producing bonding thereof to said body member.

7. The method in accordance with claim 1 wherein said molding material is a resin having cross-lin-kable groups, and wherein said solidification thereof is accomplished at least in part by cross-linking of said resin.

8. The method in accordance with claim" 1 wherein said molding material is a partially polymerized resin formulation and wherein said solidification thereof is accomplished at least in part by polymerization of said formulation.

'9. The method in accordance with claim 1 wherein said mold surface is metallic.

'10. The method in accordance with claim 1 in which said preformed body member is applied with suflicient pressure to distribute substantially uniformly said molding material over said mold surface to achieve a substantially uniform thickness.

11. In a method for making retroreflective composite synthetic plastic sheeting, the steps comprising:

(A) depositing a hardenable molding material upon a mold surface having an array of minute, contiguous cube corner recesses therein, each of said recesses having a maximum side edge dimension of less than about 0.010 inch, said molding material being essentially transparent and sufficient in amount and fluidity to essentially completely fill said recesses under the conditions of operation;

(B) applying a length of flexible, essentially transparent synthetic plastic sheet material having substantially smooth surfaces to said molding material on said mold surface under sufficient pressure to effect intimate surface contact therebetween, said application being with suflicient pressure to distribute substantially uniformly the molding material over the mold surface to achieve a substantially uniform thickness;

(C) subjecting said molding material to conditions suflicient to effect substantial solidification thereof and bonding to the adjacent surface to said sheet material to form a composite structure therewith;

(-D) removing said composite structure from said mold surface; and

(E) depositing a reflective coating on the faces of said cube corner formations to provide retroreflective sheeting comprising a body portion provided by said sheet material and having a substantially smooth front surface, and a multiplicity of minute cube corner formations corresponding to said recesses and closely spaced about and projecting from the opposite surface of said body portion, said close spacing substantially avoiding any smooth areas between said cube corner formations, so that those light rays entering said sheeting through the front surface of said body portion predominantely pass through -3,810,804 11 12 .and into saidcube. corner forrnations by which they References, Cited are reflected back through'the body portion along n i Y STATES PATENTS.

path substantially parallel to the pathro f entry; ,lll. M N v l i 1 1? method n js r'snls a mz i-i hmi r Jun q s 0 there. 'ar'efineludedthe additional.stepsmofdepositlngta 5 fl,- -v--- 0.1Q adhesive layer on said reflective coating and loosely adher- ,1 wi e- -r 65 '305 ing a removable piece of sheet material onr sai dj adhe'siye layer, whereby saidremoval sheet material-may thereafter be removed to adhere said retroreflectivematerial to a substrate. v if I .13., The method inmaccordan eerwith claim 11 wherein said reflective coating i sflrnetallic'andwhereimihereds included the, additional stepwof depositing,ra layenofi resin on said, metallic coating .to provide protection therefor.

UNITED STATES PATENT OFFICE h QERTIF ICATE OF CORRECTION Patent NO. 3 810 804 D t May 14, 1.974

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:'

Column 10 line 7, "layers" should be 1ayer--;

column 10, line 18, "mildin should be mo1ding;

Column 10, 1ine59, "to said sheet" should be -of said sheet";

Column 11, line; a, "frerhova 'lllshould be'- ovab1 Signed ahd sealed this 3rd dsyof December 1974.

v (SEAL) Attest:

McCOY M. GIBSON JR. j v, c. MARSHALL-BAND} Attesting Officer v Commissioner of Patents FORM PO-1050 (Q-6 I I uscoMM-oc scan-P09 v LLS. GOVERNMENT PRINTING OFFICE; 19.9 0-3693! 

